This invention relates to the manufacture of flexible bags and particularly to the manufacture of draw tape bags from thermoplastic films wherein the draw tape is in the form of a thickened strip of thermoplastic material separably integral with the bag body.
Bags made of plastic film such as thin polyethylene film have been used in various sizes. Small bags are used in the packaging of sandwiches and the like; larger bags are used as shopping bags and even larger bags are used for containing trash. The present invention is particularly related to the small or medium size bags where the loading of the bag is not particularly heavy but a tight draw closure is desired.
A particularly advantageous closure for such bags includes a draw band or tape constructed from the same polyethylene material. Draw tape bags of this type have been known for several years and are described in various patents such as, for example, U.S. Pat. No. 3,029,583--Piazzi and U.S. Pat. No. 3,412,032--Jortikka which are examples of draw tape bags of the moderate size shopping bag type. Bags of this type are formed by two pliable plastic sheets joined to one another on three sides and open at a fourth. A tubular hem is provided at the open end of each sheet and contains a pliable thermoplastic strip. A hole intermediate the ends of each hem exposes the strip in the hems allowing them to be pulled through the openings and used as a handle while simultaneously closing the open mouth of the bag. A similar type bag is disclosed in U.S. Pat. No. 4,624,654 Boyd et al. In the foregoing patents the draw tapes are separate from the plastic bags. U.S. Pat. No. 3,738,568--Ruda discloses a plastic bag with a draw band separably integral with the bag body and U.S. Pat. No. 3,982,687--Auer et al discloses a thermoplastic bag where the detachable strap is a looped portion of one sidewall of the bag. A hemless draw band bag with the draw band being a folded over double-ply portion of the bag body partially separated from the body with relatively minute tear points connecting it to the body is disclosed in application Ser. No. 947,717, filed Dec. 30, 1986 by Paul V. Osborn entitled "Draw Band Bag" and assigned to the same assignee as the present invention.
It is an object of the present invention to provide a thermoplastic bag with an integral draw strip which is extruded concurrently with the thermoplastic film of the bag body and has a thicker dimension than the thermoplastic film.